A number of prosthetic shoulder joints have been developed to facilitate shoulder movement in a prosthetic system. These generally consist of two friction joints in close proximity to replace the anatomical motions of flexion-extension and abduction-adduction. The user must overcome this friction to position the joint. When the friction is high, the user requires excessive force to reposition. When it is too low, inadvertent slippage may cause a problem. Furthermore it is impossible to use these joints in the free-swing mode that greatly increases comfort during walking.
Although there are some prosthetic knee joints that provide the user with a free-swing mode in the knee joint, such as those described in U.S. Pat. No. 6,764,520 issued on Jul. 20, 2004 to Deffenbaugh et al., U.S. Pat. No. 4,614,518 issued on Sep. 30, 1986 to Lehneis et al. and U.S. Pat. No. 4,520,512 issued on Jun. 4, 1985 to Lehneis et al., these free-swing knee joints are not suitable for a shoulder joint. The free-swing modes in these prosthetic knee joints are not feasible for use in a shoulder joint because the free-swing mode is either on or off and when on, it is completely free to swing without any intermediary locking positions.
Prior prosthetic shoulder joints also do not provide a means for efficiently managing control cables necessary to activate and control the movements of the prosthesis. Such cables just hang loose and get caught up in or tangled around the prosthesis during movement of the joint.